The present invention relates generally to the field of material processing, and more particularly to a plasma apparatus and a method for detecting a process endpoint.
It is desirable to have a non-intrusive, sensitive etch endpoint apparatus and method to detect the exposure of a desired sublayer in an item being etched. Several techniques have been demonstrated for etch endpoint detection, including optical emission spectroscopy, plasma impedance monitoring, and laser interferometry. However, all of these techniques fail to provide sufficient sensitivity when there is a very low pattern etch factor, i.e., a low percentage of the item's surface is exposed to the etching medium. Additionally, some of these techniques require considerable signal averaging to improve the signal-to-noise ratio. The use of these methods thus results in a slower response to etch plasma compositional changes and a slower response to endpoint indicia in the plasma.
The failure of the prior art techniques for detecting endpoint in the presence of very low pattern factors provide a significant impediment to the semiconductor industry drive for faster circuit devices. Such faster circuit devices require smaller component dimensions which often result in very low wafer pattern densities. At the same time, faster etch processes result in the need for more precise endpoint control with a fast endpoint detection response.
Alternatively, it is desirable to be able to detect with precision the coverage of a low pattern factor area in a deposition process. Similar detection problems to those noted above are encountered in this type of processing.
The invention as claimed is intended to remedy the above-described etch endpoint and deposition endpoint detection problems and limitations that arise when low pattern factors are present.
The advantages offered by the present invention are that extremely low pattern factor endpoints can be detected with high resolution and a very fast response. This endpoint detection can be utilized when etching, for example, a top layer through to another layer therebelow, when those two layers have different work functions. Likewise, this invention can be used when depositing a top layer on to another layer, where those two layers have different work functions. Accordingly, this invention can be used to detect endpoint when etching or depositing a top layer of metal, semiconductor, or insulator material through or on to another layer therebelow of metal, semiconductor or insulator material which layer has a different work function. This invention is particularly advantageous in that it is essentially independent of the plasma composition, it has a high detection signal-noise ratio, and it is not highly wavelength sensitive.